The bistros of Lyons are a potato lover's paradise. This version, typical of the simple potato and onion mixtures typically served with roast meats or steak, is quick and easy to prepare.

Boil or steam the potatoes until tender and mashable. Drain. Let the poratoes rest for a few minutes. Coarsely mash with a fork, leaving a few irregular chunks.

Preheat the broiler.

Halve the onions lengthwise; cut each half into thin half-moon rounds.

In a large skillet, melt 1/3 of the butter (or margarine) over medium-high heat. Add the onions and saute until soft and golden, about 10 minutes.

Add 1/3 more of the butter (or margarine) and melt. Add the potatoes, season generously with nutmeg, salt and pepper, and cook, tossing the mixture about 2 or 3 more minutes.

Transfer the mixture to a gratin dish. Smooth with the back of a large spoon, then dot with the remaining butter (or margarine).

Brown lightly under the broiler.

Serve immediately.